In history class, the girl to boy ratio is $4$ to $10$. If there are a total of $70$ students, how many girls are there?
Explanation: A ratio of $4$ girls to $10$ boys means that a set of $14$ students will have $4$ girls and $10$ boys. A class of $70$ students has $5$ sets of $14$ students. Because we know that there are $4$ girls in each set of $14$ students, the class must have $5$ groups of $4$ girls each. There is a total of $20$ girls in history class.